1. Field of the Invention
The present invention relates to liquid crystal display apparatuses, and particularly to techniques that are effective for discharging charges from pixels at the time of power-off or the like.
2. Description of the Related Art
In a liquid crystal display apparatus, if power is turned off with charging remaining at pixels, the liquid crystal display apparatus is left for a long period with a DC voltage applied to a liquid crystal layer. This causes image sticking, which results in reduction of the lifespan (reliability) of the liquid crystal. Therefore, at the time of power-off, charges remaining at the pixels (remaining charges) must be discharged quickly.
In a first method according to the related art, in order to discharge remaining charges at the time of power off, before the liquid crystal display apparatus is powered off, a white signal (or a black signal) is written by controlling timing of writing to the panel. In a second method according to the related art, reduction in a power supply voltage is monitored, switching transistors of the pixels are simultaneously turned on according to the result of monitoring, and the remaining charges are discharged via discharging switches provided in association with a plurality of data signal lines (hereinafter referred to as signal lines) connected to the pixels.
According to the first method, timing pulses for writing data to the panel must be generated, and timing of power-off after the writing must be managed. This requires complex timing control.
The second method is described in Japanese Patent Laid-Open No 2004-226597. According to the second method, without requiring complex timing control, remaining charges can be discharged quickly. According to Japanese Patent Laid-Open No 2004-226597, a liquid crystal display apparatus includes a detecting circuit configured to detect reduction in a power supply voltage in the liquid crystal display apparatus and to output a detection signal, and a plurality of discharging elements connected individually in series with a plurality of data lines, configured to turn on according to the detection signal so that the data lines are discharged. Furthermore, when the detecting circuit has detected power-off of the power supply voltage, a gate control circuit controls a voltage applied to the gates of a plurality of switching transistors so that the switching transistors are simultaneously turned on.